It is known to determine the position of an object using optical metrology, which includes the process of using reflected light to identify or at least estimate the position of an object in a region.
Optical metrology is one way of obtaining the real-time position of a moving object, for example in gaming, robotics, human-computer interaction applications and in medical applications. Regarding the latter, optical metrology has been found to be particularly useful in radio therapeutic apparatuses where it is important to determine the position of a remote object with a high degree of accuracy. One example is that of a multi leaf collimator (MLC) which is a device used in a linear accelerator (Linacs) to shape a beam of X-ray radiation to appropriately treat tumours. The position of each leaf must be accurately determined but from a remote position to avoid exposure to the X-rays. The use of a scanning light source and reflectors for identifying the leaf positions has been described in WO2011/107112.
A fast and accurate three-dimensional (3D) tracking and position measurement method is described in http://adriaticresearch.org/Research/pdf/Tracking_OMEMS2008.pdf.
Here, two sets of two-dimensional (2D) micro-electromechanical (MEM) scanning mirrors are required to track an object in 3D space, regardless of the method used to mark the devices to the system, e.g. using reflectors or infra-red (IR) sources. However, 2D MEM devices are relatively expensive, particularly compared with one-dimensional (1D) MEM devices and furthermore require additional circuitry to drive and track their orientation.